The present invention relates to the field of optical shutters and, particularly, pertains to optical shutters which operate in the near-infrared and/or visible wavelength regions. More specifically, this invention pertains to optical shutters comprising an organic free radical compound, wherein the organic free radical compound forms an oxidized or a reduced product having a change in absorption in a near-infrared or a visible wavelength region as a result of a photo-induced electron transfer reaction of the free radical compound.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the quantity and speed of data communications over fiber optics systems rapidly increases due to the growing demand from Internet usage and other communications, all-optical switching systems are of increased interest to overcome the high cost and slow switching speeds of conventional switches. These conventional switches include, for example, various mechanical switches, electro-optic switches, and thermo-optic switches, such as, for example, described in U.S. Pat. Nos. 5,732,168 and 5,828,799, both to Donald. In particular, the increased complexity and cost of switching systems which involve switching from an optical signal to an electrical signal and then back to an optical signal have increased the level of interest in all-optical switches.
An all-optical switch typically switches an optical signal from one output port to another. This is typically accomplished by applying an input pump signal from a pump laser source to cause the optical signal to be selectively switched. The switch is responsive to the laser pump signal to selectively switch the light of the optical signal to one or the other of the output ports.
A variety of approaches are known for making all-optical or hybrid optical switches, such as, for example, described in U.S. Pat. Nos. 5,905,587 to Maeno et al.; U.S. Pat. No. 5,923,798 to Aksyuk et al.; U.S. Pat. No. 5,970,185 to Baker et al.; U.S. Pat. No. 5,841,912 to Mueller-Fiedler et al.; U.S. Pat. No. 5,757,525 to Rao et al.; U.S. Pat. No. 5,872,648 to Sanchez et al.; U.S. Pat. No. 5,091,984 to Kobayashi et al.; U.S. Pat. No. 5,406,407 to Wolff; U.S. Pat. No. 5,740,287 to Scalora et al.; U.S. Pat. No. 5,960,133 to Tomlinson; and U.S. Pat. No. 5,539,100 to Waslielewski et al. For example, as described in U.S. Pat. No. 5,943,453 to Hodgson, one basic configuration for an all-optical switch is a Mach-Zehnder interferometer which includes a first fiber optic input arm for receiving an input optical signal and a second fiber optic input arm for receiving a switching pump signal. The input arms are fused together to form a first coupler which subsequently branches out into two intermediate arms. The first coupler splits the input light signal into equal portions which then enter the two intermediate arms. The two intermediate arms are once again fused to form a second coupler which branches into two output arms. After traveling through the two intermediate arms, the two signals are recombined by the second coupler. If the two signals are in phase at the second coupler, then all the light is coupled into a first one of the two output ports. If the two signals are completely out of phase, then the light is coupled into the other of the two output ports. The reliability of the Mach-Zehnder interferometer for optical switching is typically sensitive to temperature-dependent effects.
The need for improved optical switches is increased by the use of wavelength add/drop multiplexing (WADM) which converts the optical signal in the optical fiber into, for example, 16 signals at 16 different wavelengths in a near-infrared range of about 1540 to 1560 nm, as, for example, described in Bell Labs Technical Journal, January-March 1999, pages 207 to 229, and references therein, by Giles et al.; and in U.S. Pat. No. 5,959,749 to Danagher et al. There is about 1 nm between the wavelength channels. The primary function of the optical switch is to add and/or drop optical signals from the multiple wavelengths traveling through the optical fiber. It would be highly desirable to have arrays of optical switches to handle the optical signals from multiple wavelengths per optical fiber and from multiple optical fibers, such as up to 100xc3x97100 or greater optical switch arrays. Also, it would be highly desirable if the response time for the optical switch is ultrafast, such as I nanosecond or less.
It would be advantageous if an all-optical switching system were available which avoided the complexity and cost of hybrid electro-optic and other systems while increasing the speed of the switching times from the millisecond range to the nanosecond or picosecond ranges.
An organic free radical compound where the excited state is an excited state from the free radical ground state may have a rapid internal conversion from this excited state back to the ground state with a concomitant production of heat in a time scale of as low as 1 picosecond or less. In one example of this, an organic radical cation compound absorbs photons in the presence of a thermochromic compound, converts the absorbed photons to heat in less than 1 nanosecond, and causes a change in absorption due to heat-induced changes in the thermochromic compound, as described in PCT International Publication No. WO 98/54615, titled xe2x80x9cOptical Shutter Devicexe2x80x9d and published Dec. 3, 1998, to Carlson. The present invention utilizes an organic free radical compound which undergoes a photo-induced electron transfer reaction which causes changes in absorption due to the oxidation or the reduction of the free radical compound. This photo-induced electron transfer reaction may occur faster and with higher efficiency than internal conversion of the absorbed photons to heat or, alternatively, may have a similar or slightly lower speed and efficiency than this internal conversion to heat so that both electron transfer and heat formation processes occur.
One aspect of the present invention pertains to an optical shutter comprising an organic free radical compound in which the free radical compound is characterized by forming an oxidized or reduced product having a change in absorption in a near-infrared wavelength region as a result of a photo-induced electron transfer reaction of the free radical compound. In one embodiment, the free radical compound is a radical cation, preferably an aminium radical cation, and most preferably, the radical cation is tris (p-dibutylaminophenyl) aminium hexafluoroantimonate. In one embodiment, the free radical compound is a radical anion, preferably an anthrasemiquinone radical anion.
In one embodiment of the optical shutter of this invention, the free radical compound is a radical cation, and the optical shutter further comprises a radical anion. In one embodiment, the free radical compound is a radical anion, and the optical shutter further comprises a radical cation. In one embodiment, the free radical compound comprises one or more radical cations and one or more radical anions, and the change in absorption results from a photo-induced electron transfer reaction of at least one of the one or more radical cations and of at least one of the one or more radical anions. In one embodiment, the free radical compound comprises a salt of a radical cation and a radical anion.
In one embodiment of the optical shutter of the present invention, the change in absorption is greater than 0.1, preferably greater than 0.5, and more preferably greater than 1.5. In one embodiment, the near-infrared wavelength region of the change in absorption is from 700 to 1000 nm. In one embodiment, the near-infrared wavelength region of the change in absorption is from 1000 to 1400 nm, preferably from 1400 to 1600 nm, more preferably from 1520 to 1580 nm, and most preferably from 1500 nm to 1700 nm.
In one embodiment of the optical shutter of this invention, the photo-induced electron transfer reaction occurs in less than 1 nanosecond after absorption of photons by the free radical compound, preferably occurs in less than 0.1 nanoseconds, more preferably occurs in less than 0.01 nanoseconds, and most preferably occurs in less than 0.001 nanoseconds or less than 1 picosecond after absorption of photons by the free radical compound.
In one embodiment of the optical shutter of the present invention, the photo-induced electron transfer reaction is an oxidation of the free radical compound. Suitable electron transfer reactions include, but are not limited to, an one-electron oxidation of the free radical compound, a two-electron oxidation of the free radical compound, an one-electron reduction of the free radical compound, and a two-electron reduction of the free radical compound.
In a preferred embodiment of the optical shutter of this invention, the change in absorption is reversible. In one embodiment, the reversible change in absorption is induced by heat. In one embodiment, the reversible change in absorption is induced by radiation selected from the group consisting of: ultraviolet radiation, visible radiation, and infrared radiation; and, preferably, the reversible change in absorption is further induced by the presence of oxygen. In one embodiment, the reversible change in absorption occurs at less than 50xc2x0 C. in the absence of radiation. In one embodiment, the reversible change in absorption occurs in less than 1 second, preferably occurs in less than 10 milliseconds, more preferably occurs in less than 1 millisecond, and most preferably occurs in less than 0.1 milliseconds.
In one embodiment of the optical shutter of the present invention, the photo-induced electron transfer reaction is induced by ultraviolet radiation. In one embodiment, the photo-induced electron transfer reaction is induced by visible radiation, and preferably is induced by near-infrared radiation. In one embodiment, the photo-induced electron transfer reaction is induced by absorption of photons by a free radical ground state of the free radical compound.
In one embodiment of the optical shutter of this invention, the optical shutter further comprises a metallized layer on at least one side of a layer comprising the free radical compound of the optical shutter. In one embodiment, the metallized layer comprises aluminum.
One aspect of the present invention pertains to an optical shutter comprising an organic radical cation compound in which the radical cation compound is characterized by forming an oxidized or a reduced product having a change in absorption in a near-infrared wavelength region as a result of a photo-induced electron transfer reaction of the radical cation compound. In one embodiment, the optical shutter further comprises a radical anion.
Another aspect of this invention pertains to an optical shutter comprising an organic radical anion compound in which the radical anion compound is characterized by forming an oxidized or a reduced product having a change in absorption in a near-infrared wavelength region as a result of a photo-induced electron transfer reaction of the radical anion compound. In one embodiment, the optical shutter further comprises a radical cation.
Still another aspect of the present invention pertains to an optical shutter comprising one or more radical cations and one or more radical anions, wherein at least one of the radical cations and at least one of the radical anions is characterized by forming an oxidized or a reduced product having a change in absorption in a near-infrared wavelength region as a result of a photo-induced electron transfer reaction of at least one of the one or more radical cations and at least one of the one or more radical anions.
Another aspect of the present invention pertains to an optical shutter comprising an organic free radical compound, preferably a radical cation compound or a radical anion compound, in which the free radical compound is characterized by forming an oxidized or a reduced product having a change in absorption in a visible and/or a near-infrared region as a result of a photo-induced electron transfer reaction of the free radical compound, wherein the change in absorption is reversible. In one embodiment, the optical shutter is utilized in an optical switch for a fiber optics communications channel.
Yet another aspect of this invention pertains to an optical shutter comprising an organic free radical compound in which the free radical compound is characterized by forming an oxidized or a reduced product having a change in absorption in a visible wavelength region as a result of a photo-induced electron transfer reaction of the free radical compound. In one embodiment, the change in absorption is reversible. In one embodiment, the change in absorption is reversible, and the optical shutter is utilized in a viewing lens of an eyewear device.
Another aspect of the present invention pertains to an optical shutter comprising an organic free radical compound in which the free radical compound is characterized by forming an oxidized or a reduced product having a change in absorption in a visible or a near-infrared wavelength region as a result of a photo-induced electron transfer reaction of the free radical compound. In one embodiment, the optical shutter is utilized in a laser protection device for protection of eyes or sensors from a source of laser radiation. In one embodiment, the optical shutter is utilized in a security protection system based on detecting the change in absorption upon exposure of the optical shutter in the security protection system to high intensity radiation selected from the group consisting of: ultraviolet radiation, visible radiation, and infrared radiation.
As will be appreciated by one of skill in the art, features of one aspect or embodiment of the invention are also applicable to other aspects or embodiments of the invention.
The optical shutters of the present invention provide superior speed of response, such as a response time of 1000 picoseconds or less, to the incident radiation, and are particularly useful in systems where an all-optical shutter mechanism is desirable.
The term xe2x80x9corganic free radical compounds,xe2x80x9d as used herein, pertains to organic compounds which comprise at least one free unpaired electron on a neutral atom, such as, for example, a carbon atom, a nitrogen atom, or an oxygen atom, in the ground state of the organic compound. Suitable organic free radical compounds for the optical shutters of the present invention include neutral organic free radicals, organic free radical cations, and organic free radical anions. For purposes of brevity, the terms xe2x80x9corganic free radical cationxe2x80x9d, xe2x80x9corganic radical cationxe2x80x9d, and xe2x80x9cradical cationxe2x80x9d are used interchangeably herein. The word xe2x80x9ccation,xe2x80x9d as used herein, pertains to a positively charged atom in a molecule, such as, for example, a positively charged nitrogen atom. Similarly, the terms xe2x80x9corganic free radical anionxe2x80x9d, xe2x80x9corganic radical anionxe2x80x9d, and xe2x80x9cradical anionxe2x80x9d are used interchangeably herein. The word xe2x80x9canion,xe2x80x9d as used herein, pertains to a negatively charged atom in a molecule, such as, for example, a negatively charged oxygen atom. It should be noted that the free unpaired electron and the positive and negative charges of the organic free radical compounds may be localized on a single atom or shared among more than one atom.